const OSC8_CLOSE = "\x1b]8;;\x1b\\";
// SGR, cursor markers, OSC, and other non-printing controls can split marker text.
const CONTROL_RE = /\x1b(?:\[[0-?]*[ -/]*[@-~]|[\]_^P][^\x07\x1b]*(?:\x07|\x1b\\)|[()][A-Za-z0-9])/g;

function localLink(reference: string | undefined): string | undefined {
	if (!reference || /[\x00-\x20\x7f]/.test(reference)) return undefined;
	try {
		const url = new URL(reference);
		return url.protocol === "file:" && !url.hostname ? url.href : undefined;
	} catch {
		return undefined;
	}
}

/** Decorate render output only. Original controls, cursor positions, and editor text stay intact. */
export function renderDraftImageLinks(
	lines: readonly string[],
	resolveReference: (marker: string) => string | undefined,
): string[] {
	return lines.map((line) => {
		// Do not nest links supplied by another editor.
		if (line.includes("\x1b]8;")) return line;
		const offsets: number[] = [];
		let plain = "";
		let position = 0;
		for (const control of line.matchAll(CONTROL_RE)) {
			for (; position < control.index; position += 1) {
				offsets.push(position);
				plain += line[position];
			}
			position = control.index + control[0].length;
		}
		for (; position < line.length; position += 1) {
			offsets.push(position);
			plain += line[position];
		}
		let result = "";
		let end = 0;
		for (const match of plain.matchAll(/\[Image #\d+\]/g)) {
			const reference = localLink(resolveReference(match[0]));
			if (!reference) continue;
			const start = offsets[match.index];
			const last = offsets[match.index + match[0].length - 1];
			if (start === undefined || last === undefined) continue;
			const stop = last + 1;
			result += line.slice(end, start) + `\x1b]8;;${reference}\x1b\\` + line.slice(start, stop) + OSC8_CLOSE;
			end = stop;
		}
		return result + line.slice(end);
	});
}